[Solved]-Add custom tooltip for x axis label on hover action-Highcharts

Use a basic function instead of an arrow one and refer to a chart by this keyword:

mouseover: function(e) {
    this.chart.renderer.label("tooltip text", e.x, e.y, 'rectangle').css({
            color: '#FFFFFF'
        })
        .attr({
            fill: 'rgba(0, 0, 0, 0.75)',
            padding: 8,
            r: 4,
        })
        .add()
        .toFront();
}

Live demo: http://jsfiddle.net/BlackLabel/dfazcwyr/